1. Field of the Invention
The present invention relates to a cooling device for a battery pack composed of a plurality of rechargeable batteries arranged in parallel with a cooling medium path interposed therebetween.
2. Description of the Related Art
As a battery pack composed of a plurality of rechargeable batteries, the following type of battery pack is conventionally known so as to prevent a battery temperature from being increased due to heat emission caused by charge and discharge to decrease a battery output, a charge/discharge efficiency or a battery lifetime. A plurality of rechargeable batteries are arranged in parallel with a cooling medium path interposed therebetween. Then, a cooling medium feeding device for feeding a cooling medium to the cooling medium path is provided for the battery pack (for example, see Japanese Patent Laid-Open Publication No. 2001-167803).
As such a type of battery pack, the following battery pack has also been conceived. As shown in FIG. 10A, a rechargeable battery 22 is composed of a plurality of prismatic cells 23 by connecting their short side faces with each other. A plurality of thus constituted rechargeable batteries 22 are arranged in parallel so as to interpose cooling medium paths 24 for allowing a cooling medium to horizontally pass therethrough between the long side faces of the rechargeable batteries 22, thereby constituting a battery pack 21. A feeding hood 25 for feeding the cooling medium is connected to one end of the cooling medium path 24 of the battery pack 21, whereas an exhaust hood 26 is connected to the other end of the cooling medium path 24. In such a structure, the cooling medium is fed in a direction indicated with arrows on the cooling medium path 24 as shown in FIG. 10A.
In addition, the following type of battery pack is also known. In the battery pack, a container is provided so as to house a plurality of rechargeable batteries therein. The container is also thermally connected to circumferential wall surfaces of the rechargeable batteries so as to be in contact therewith. A heat pipe is provided for the container so as to externally dissipate heat transferred from the rechargeable batteries (for example, see Japanese Patent Laid-Open Publication Nos. 2001-76771 and 2002-134177).
In the cooling device of the battery pack 21 having the structure as shown in FIG. 10A, if the cooling medium is allowed to pass through the cooling medium paths 24 between the rechargeable batteries 22 in the direction indicated with the arrows, a temperature of the cooling medium is elevated as the cooling medium passes through the cells 23 to cool them. When the cooling medium reaches the exhaust hood side, the cooling medium has lowered cooling performance. As a result, as shown in FIG. 10B, a temperature of the cell 23 on the downstream side of a flow direction of the cooling medium becomes higher than that of the cell 23 on the upstream side. Thus, a temperature variation ΔT between the cells 23 in the rechargeable battery 22 is increased. A variation in SOC between the cells 23 is also increased to elevate the maximum temperature Tmax of the cells 23 in the battery pack 21, thereby adversely affecting the lifetime of the battery pack 21.
Moreover, in the structure of externally dissipating the heat generated by the rechargeable batteries housed in the container through the heat pipe as disclosed in Japanese Patent Laid-Open Publication Nos. 2001-76771 and 2002-134177, a large number of heat pipes or a large number of heat collector members are necessitated if cooling performance to efficiently cool all the rechargeable batteries is desired to be obtained. As a result, a space efficiency is disadvantageously lowered to increase the cost. Even though, it is difficult to uniformly cool each of the parts in the rechargeable battery.